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6 S4 routing algorithm in a nutshell Theoretical foundation on compact routing [SPAA ’ 01] –Worst-case routing stretch is 3 –O( ) state per node Node classification –beacon nodes nodes –regular nodes Know how to route to the beacons Node clusters –Each regular node d has a cluster, in which each node knows how to route to d. –Radius is the distance to the closest beacon. –Different from hierarchical routing.

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8 Protocol Design Challenges How to maintain routing state inside a cluster? –Flooding is expensive How to maintain routing state for beacon nodes? –Unreliable broadcast may affect routing stretch Routes to beacons may not be optimal. Unnecessarily long radius How to provide resilience against node/link failure? –Transient failure –During routing state convergence

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13 Questions to answer Does S4 achieve small stretch? –routing stretch and transmission stretch –Average case vs worst case Does S4 achieve small state? How does S4 perform under failure? How well does S4 work in a real testbed? Many others in the paper..

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18 Testbed Deployment 42 mica2 motes –915MHz radios –11 of them (called gateway motes) are connected to MIB600 Ethernet board, powered by the adapters –31 of them are powered by batteries Reduce power level to create multi-hop topology –A link between two nodes exists if the packet delivery rates of both directions are above 30% –The network diameter is around 4 to 6 hops.